Method of recovering pigment



April 22, 1941.

B. MARQUIS METHOD OF RECOVERING PIeMEN'r Filed Nov. 21, 1938 INVENTOR BYRoN mancwls BY 7] ATTORNW ,fedintoth Patented Apr. 22, 1941 UNITED STATES PATENT" OFFICE Y 2,239.49: Gm I Byron Marquis, Westiieid. N. 3., assignor to Intereheniicai corporation, New York, N. Y., a corporation of Ohio Application November 21, 19st, Serial No. 241,716

Wet slurriesofpigmentofthisparticlesizecan ordinarily, and most economically, be obtained by finewet grinding and wet classification to the desired particle size. However, on filtering such mgments, and then drying them. it is found that the desired uniform small particle size is never obtained, apparently due to the cementing action between particles during the drying operation.

I have discovered that dry pigments of uniformly fine texture can be obtained from arwater slurry, by subjecting the slurry to centrifugal action,forcingthepigment intoawaterimmiscible liquid heavier than water (such as carbon tetrachloride or trichloroethylene). In this process, the wet pigment particles, as they hit the organic liquid, are simultaneously forced into the liquid bycentrlfugalforce,anddrledbytheflltering actionoftheliquidonthewater. Thepigment particles do not cement to each other when the organic vehicle is removed by heat. leaving a powderwiththeuniformflneparticlesizeof the original wet pigment.

The invention can be best understood by re- 7 .bhllllil'lf 1,.2and3showthreestagesofmyprocess. Fig. 1,theheavy liquid ll isshownbeing e rotating bowl ll of a conventional centrifuge l2 comprising the rotating bowl prowith an inlet and overflow opening II, dump opening I4, and an overflow chamber and lighter, is kept to the center of the bowl,

while the heavier pigment passes through the liquidtothe outsideedgeofthebowi. Thewater When the organic solvent reaches the overflow piete.thecent'rifugeisl pped.mdthepigment ins. Since the organic solvent flows while the pigment doa not, the bulk of the separation occurs at once. The solvent may befiltered, but is preferably returned to the centrifuge to start another cycle without filtration. The Pigment is very readily dried of the small amount of solvent remaining in it.

Any organic liquid may be used which is immiscible with and heavier than water. which is ,asshown-inmI.theoperafloniscom-' non-reactive with and lighter than the pigment used, and which may be removed from the pigment without causing cementing. Carbon tetrachloride and trichloroethylene are particularly desirable.

The pigment must obviously be sufliciently heavier than the water so that it will centrifuge out of it. Practically all pigments may be dried by my method except certain light organic toners.

In addition, care must be taken-with certain or. ganic colors that they are insoluble in the solvents.- I have successfully dried lithopone, zinc sulfide, chrome yellow, titanium and many other pigments, in every case obtaining a desirable nonagglomerated structure.

My process-can also be used for removing pigment from suspensions in organic liquids which have a 'cementing actionmn the pigment? For example, in analyzing a paint, where a clean separation of pigment and oil is desired, the paint my be reduced to very thin consistency with light petroleum naphtha, and centrifuged. using distilled water as the heavy filtering liquid, to set a clean separation of the pigment from the paint vehicle.

I claim:

1. Die method of drying a water wet pigment powder which comprises feeding sumcient water immiscible volatile organic liquid heavier than water and having no cementing action on the powder into the bowl of a running centrifuge to form a layer therein, feeding a water pigment slurry into the bowl, whereby the pigment through said layer and the water overflows, continuing the operation'until the bowl is full of pigment and organic liquid, then removing the centrifugalactionthroughalayerofwaterim miscible volatile organicliquidheavierthanwaterandhavingnocementingactioncnthepiginto the dump openmt, separating the water from the organic 5 the organic liquid.

liquid heavier than water and having no cementing action on the pigment, thereby separating the water from the organic liquid and pigmenigand recovering the pigment from its mixture with BYRON MARQUIS. 

